Not Applicable
1. Field of the Invention
The present invention relates generally to a method for manufacturing a heat transfer element that is capable of modification and control of the temperature of a body or of a selected body organ. More particularly, the invention relates to a method for manufacturing an intravascular apparatus including a heat transfer element for controlling body and organ temperature. The invention is also directed to the resulting heat transfer element.
2. Background Information
Organs in the human body, such as the brain, kidney and heart, are maintained at a constant temperature of approximately 37xc2x0 C. Hypothermia can be clinically defined as a core body temperature of 35xc2x0 C. or less. Hypothermia is sometimes characterized further according to its severity. A body core temperature in the range of 33xc2x0 C. to 35xc2x0 C. is described as mild hypothermia. A body temperature of 28xc2x0 C. to 32xc2x0 C. is described as moderate hypothermia. A body core temperature in the range of 24xc2x0 C. to 28xc2x0 C. is described as severe hypothermia.
Hypothermia is uniquely effective in reducing brain injury caused by a variety of neurological insults and may eventually play an important role in emergency brain resuscitation. Experimental evidence has demonstrated that cerebral cooling improves outcome after global ischemia, focal ischemia, or traumatic brain injury. For this reason, hypothermia may be induced in order to reduce the effect of certain bodily injuries to the brain as well as other organs.
Catheters have been developed which are inserted into the bloodstream of the patient in order to induce total body hypothermia. For example, U.S. Pat. No. 3,425,419 to Dato describes a method and apparatus of lowering and raising the temperature of the human body. Dato induces moderate hypothermia in a patient using a metallic catheter. The metallic catheter has an inner passageway through which a fluid, such as water, can be circulated. The Dato catheter has an elongated cylindrical shape and is constructed from stainless steel. For example, Dato suggests the use of a catheter approximately 70 cm in length and approximately 6 mm in diameter. It is clear that the Dato device has numerous limitations. For example, such a catheter would likely be inflexible and unable to navigate a tortuous vasculature.
Cooling helmets or head gear have also been used in an attempt to cool only the head rather than the patient""s entire body. However, such methods rely on conductive heat transfer through the skull and into the brain. One drawback of using conductive heat transfer is that the process of reducing the temperature of the brain is prolonged. Also, it is difficult to precisely control the temperature of the brain when using conduction due to the temperature gradient that must be established externally in order to sufficiently lower the internal temperature. From a practical standpoint, such devices are cumbersome and may make continued treatment of the patient difficult or impossible.
Selected organ hypothermia has been accomplished using extracorporeal perfusion, as detailed by Arthur E. Schwartz, M.D. et al., in Isolated Cerebral Hypothermia by Single Carotid Artery Perfusion of Extracorporeally Cooled Blood in Baboons, NEUROSURGERY, vol. 39, no. 3, p. 577 (September, 1996). However, external circulation of blood is not a practical approach for treating humans because the risk of infection, need for anticoagulation, and risk of bleeding is too great.
In all of the above, the devices have tended to have inelegant constructions, which have neglected some of the subtleties of hemocompatibility and flexibility. Therefore, a practical method to manufacture an apparatus, which is capable of modifying and controlling the temperature of a selected organ, satisfies a long-felt need.
In one aspect, the invention is directed towards a heat transfer device for intravascular temperature control of a patient. The device includes a flexible layer of a substantially conductive material, the flexible layer having a feature to produce mixing in fluid flowing adjacent the layer, the flexible layer and feature shaped and configured such that the flexible layer may be removed from a multi-part mold in the absence of an undercut.
Implementations of the invention may include one or more of the following. The fluid may be blood, a working fluid, or both. The flexible layer may be formed of a metal such as Fe, Ti, Ta, nitinol, stainless steel, Al, Ag, Au, Cu, and Ni, or combinations thereof. The total outside diameter of the device may be between about 6 f to 18 f, and more particularly between about 9 f to 14 f. The heat transfer device may include heat transfer segments separated by articulating joints. The articulating joints may be shaped and configured as bellows or as flexible tubes. The flexible layer may have a thermal conductivity in the range of about 0.1 to 4 W/cm-K. Each segment may have at least one feature thereon, the feature including at least two helical ridges or grooves, one of the at least two helical ridges or grooves having opposite helicity from another of the helical ridges or grooves. Alternatively, each segment may have a substantially cylindrical shape, the substantially cylindrical shape having a first half-cylinder and a second half-cylinder, the first and second half-cylinders joined at two sets of parting strips, each parting strip extending substantially parallel to an axis of the cylindrical shape; and at least two helical ridges or grooves, one of the at least two helical ridges or grooves disposed on the first half-cylinder and another disposed on the second half-cylinder. Also alternatively, each segment may have at least one feature thereon, the feature including a continuous corkscrew design. Alternatively, each segment may have at least one dimple or knob thereon. If at least two features, such dimples or knobs, or a combination thereof, are provided, the same may be are arranged in a line substantially parallel to the axis of the segment. The two may also be offset from each other relative to the axis of the segment.
In another aspect, the invention is directed towards a method of making a heat transfer device. The method includes providing a mold in a deposition apparatus, the mold having an inside shape such that a flexible continuous substantially conductive layer may be deposited in the mold and shaped, configured, and arranged to have a feature that causes mixing in a fluid flowing adjacent the layer.
Implementations of the invention may include one or more of the following. The providing step may further include the step of providing a mold that is shaped, configured, and arranged to form a layer that lacks undercuts. The feature may include varieties of the feature disclosed above. The depositing may be performed by a technique selected from the group consisting of CVD, PVD, sputtering, MBE, electroplating, and ECD.
In yet another aspect, the invention is directed towards a product formed by any of the above processes.
In yet a further aspect, the invention is directed towards a method for performing a medical procedure while managing and controlling the temperature of the patient. The method includes intravascularly inserting a catheter having a heat transfer element into a patient to be treated, the heat transfer element being formed of a flexible layer of a substantially conductive material, the flexible layer having a feature to produce mixing in fluid flowing adjacent the layer, the flexible layer and feature shaped and configured such that the flexible layer may be removed from a multi-part mold in the absence of an undercut; cooling or heating the heat transfer element to control the patient""s temperature; and performing a medical procedure during at least a portion of the time of the cooling or heating step.
Implementations of the invention may include one or more of the following. The medical procedure may be selected from the group consisting of: angioplasty, neurosurgery, cardiovascular surgery, stroke treatment, and combinations thereof.
In another aspect, the invention is directed towards a heat transfer device including a flexible mechanical layer of a metal that is shaped and configured to produce mixing in fluid flowing adjacent the layer, and a biocompatible layer of material disposed adjacent the mechanical layer.
Implementations of the invention may include one or more of the following. A protective layer may be provided that is formed of a material that is not corrosive when exposed to a working fluid, the protective layer disposed on the side of the mechanical layer opposite the biocompatible layer. A top layer of a material, chosen from the group consisting essentially of heparin, similar antithrombogenic materials and lubricious materials, may be disposed on the side of the biocompatible layer opposite the mechanical layer.
The mechanical layer may be formed of a sandwich structure including at least two layers of materials. The sandwich structure may be formed of two layers of a first material separated by a layer of a second material. The thickness of all the layers together may be less than about 1 mil in thickness. The layers of the first material may each have substantially the same thickness. The first material may be selected from the group consisting essentially of Ni, Fe, Ti, steel, Al, or other similar materials, or combinations of the same, and the second material may be selected from the group consisting essentially of Ag, Au, Cu, or other similar materials, or combinations of the same. The total diameter of the device may be between about 9 french [f] to 14 f. The heat transfer device may include heat transfer segments separated by articulating joints. The segments may be shaped and configured as helices and the joints as bellows or flexible tubes. The biocompatible coating may be selected from the group consisting essentially of Au, parylene, platinum, other similar materials, and combinations thereof. The mechanical layer may have a thermal conductivity in the range of about 0.1 to 4 W/cm-K. A protective layer may be the innermost layer, the protective layer formed of a material which is non-corrosive when exposed to a working fluid. For working fluids of saline, the protective layer may be, e.g., Au.
In another aspect, the invention may be directed to a method of making a heat transfer device, including disposing a mandrel in a deposition apparatus, the mandrel having an outside shape such that a material formed thereon is configured and arranged to cause mixing in a fluid flowing adjacent the material. Other steps include depositing a mechanical layer of a material having sufficient ductility and surface energy to substantially conform to the contours of the outside shape, depositing a biocompatible coating on the mechanical layer, and dissolving the mandrel.
Implementations of the method may include one or more of the following. Either or both of a layer of an antithrombogenic material or a lubricious material may be deposited on the biocompatible coating. A protective layer may be deposited on the mandrel so as to be the innermost layer of the device, the protective layer formed of a material which does not corrode when exposed to a working fluid, such as Au. The biocompatible coating may be selected from the group consisting essentially of Au, Pt, urethane, Teflon(copyright), other noble metals, parylene, or other similar materials or combinations thereof. The mandrel may be formed of Al, and may be formed having a shape configured and arranged such that a material formed thereon is capable of causing mixing in a fluid flowing adjacent the material. The mandrel may be formed by a technique selected from the group consisting of machining, injection molding, laser machining, hydroforming, or other similar techniques. The surface of the heat transfer device may be bombarded with nitrogen to provide a degree of antithrombogenicity either in combination with or instead of an antithrombogenic coating such as heparin. In all of the above, the depositing may be performed by a technique selected from the group consisting of CVD, PVD, sputtering, MBE, electroplating, electrochemical deposition (ECD), or other similar techniques or combinations of the above. A seed layer may be deposited on the mandrel, the seed layer formed of a material which is capable of bonding to the protective layer or to the mechanical layer. The depositing a mechanical layer may include depositing a sandwich structure. The depositing a sandwich structure may include depositing a layer of a first metal, depositing a layer of a second metal, and then depositing another layer of the first metal. The first metal may be Ni and the second metal may be Cu.
Advantages of the invention are manyfold. A highly conductive metallic heat transfer element may be manufactured conveniently. The metallic heat transfer element may retain a high degree of flexibility so as to be able to navigate tortuous vasculature. The heat transfer element has an atraumatic profile and is biocompatible.